The lamp of the type described above includes, for example, a metal vapor discharge lamp such as a metal halide lamp in which a lamp main body comprising a light emitting tube or a lamp main body comprising a light emitting tube and an airtight bulb containing the same is housed in an outer bulb that constitutes an outer shell of the lamp, and a halogen lamp in which a lamp main body having a light emitting filament and an airtight bulb containing the same is housed in an outer bulb that constitutes an outer shell of the lamp.
The existent lamp 61 with the outer bulb described above has a lamp main body 66, an outer bulb 67 housing the main body, and a base 68 attached on one end thereof as shown in FIGS. 14 and 15.
In the lamp main body 66, a light emitting tube 62 is contained in an airtight bulb 64 which is hot press bonded on one end to form a pinch seal 65, and a pair of lead wires 63 of the light emitting tube are led out of the pinch seal 65.
In the base 68, a supporting post 69 is formed for attaching the lamp main body 60 and the outer bulb 67, and a flange 70 for closing the opening end 67a of the outer bulb 67 is formed to the outer peripheral surface 69a thereof, and an insertion recess 71 for retaining the pinch seal 65 is formed in the supporting post 69.
Further, the supporting post 69 is formed to such a diametrical size that a gap 72 for filling a heat resistant adhesive is formed between the outer peripheral surface 69a thereof and the inner peripheral surface 67b of the outer bulb 67 opposed to the outer peripheral surface of the supporting post 69.
When the lamp 61 is assembled, in order that the lamp main body 66 does not tilt in a state of inserting the pinch seal 65 of the lamp main body 66 to the insertion recess 71 of the supporting post 69, a heat resistant adhesive A is filled in a gap between them and deposited over the upper surface of the supporting post 69, as shown in FIG. 16A.
Then, after depositing the heat resistant adhesive A sufficiently over the outer peripheral surface 69a of the supporting post 69, the outer bulb 67 is fitted externally so as to scrape off the peripheral surface of the adhesive A as shown in FIG. 16B, and the outer bulb 67 is fitted externally such that the opening end 67a is closed by the flange 70 of the supporting post 69, thereby filling the adhesive in the gap 72 as shown in FIG. 16C.
However, since the outer bulb 67 is transparent and the adhesive A deposited over the upper surface of the supporting post 69 is visible externally, the appearance is disfigured to worsen the commercial value.
For concealing the adhesive, a lamp with an outer bulb formed with an opaque film to the outer bulb has been proposed (refer to Patent Document 1).
In the lamp with the outer bulb, an opaque film that conceals the adhesive filled in the gap 72 is formed to the base end (near the opening end 67a) of the outer bulb 67.
However, since the base end of the outer bulb 67 is exposed to high temperature during lighting of the lamp and cooled to a room temperature when the lamp is turned off, it undergoes violent temperature change.
Accordingly, the opaque film has to be formed by using a heat resistant material having an adhesion strength to such an extent as not peeling from the surface of the outer bulb even when it is exposed to temperature change (high anchorage). For example, it is necessary to dip the outer bulb in an alumina-silica type heat resistant coating material, to coat the material to the inner peripheral surface or the outer peripheral surface and then bake the coating at a high temperature. Then, this requires not only the step of coating the heat resistant coating material but also requires a baking step.
Then, in a case of additionally installing a firing furnace for film formation in the production line for lamps or outer bulbs, this not only increases the installation cost but also results in a trouble that an installation space has to be ensured, for example, by displacing existent facilities. Even if an existent firing furnace can be utilized, it still needs an operation of re-arranging the conveying path in the line.
Further, since the baking step is additionally provided in any case, this results in a problem of being contrary to the social demand for energy saving and increasing the production cost and lowering the production efficiency.
Further, aside from the formation of the opaque film, while the inner peripheral surface 67b of the outer bulb 67 and the outer peripheral surface 69a of the supporting post 69 are secured by means of the adhesive A, the adhesion strength is lost by aging deterioration of the adhesive to even bring about a worry that the outer bulb 67 may possibly be detached when it is mounted with the end thereof on the side of the base 68 being directed upward.
Further, there are various kinds of bases for the lamps of the above mentioned type depending on the shapes of receptacles and it is necessary for assortment of plural kinds of bases even for lamps of an identical specification. Then, there has been a requirement for controlling inventory stocks of lamps with the outer bulb which are to be attached with respective kinds of bases.
Accordingly, there has been a problem that stocks of lamps with the outer bulb mounted with a certain kind of base may cause short age, whereas thereof lamps with the outer bulb mounted with other kind of bases may be overstocked.